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tutorial: Minor improvements to closures

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Brian Anderson 2012-07-02 23:04:55 -07:00
parent 2ea8922b8a
commit 90dcb59400
1 changed files with 26 additions and 20 deletions
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doc/tutorial.md
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@ -497,8 +497,7 @@ let s = "a\
Rust's set of operators contains very few surprises. Binary arithmetic
is done with `*`, `/`, `%`, `+`, and `-` (multiply, divide, remainder,
plus, minus). `-` is also a unary prefix operator (there are no unary
postfix operators in Rust) that does negation.
plus, minus). `-` is also a unary prefix operator that does negation.
Binary shifting is done with `>>` (shift right), and `<<` (shift
left). Shift right is arithmetic if the value is signed and logical if
@ -909,8 +908,7 @@ returns it from a function, and then calls it:
use std;
fn mk_appender(suffix: str) -> fn@(str) -> str {
let f = fn@(s: str) -> str { s + suffix };
ret f;
ret fn@(s: str) -> str { s + suffix };
}
fn main() {
@ -932,6 +930,15 @@ fn mk_appender(suffix: str) -> fn@(str) -> str {
}
~~~~
### Unique closures
Unique closures, written `fn~` in analogy to the `~` pointer type (see
next section), hold on to things that can safely be sent between
processes. They copy the values they close over, much like boxed
closures, but they also 'own' them—meaning no other code can access
them. Unique closures are used in concurrent code, particularly
for spawning [tasks](#tasks).
### Closure compatibility
A nice property of Rust closures is that you can pass any kind of
@ -946,25 +953,17 @@ fn call_twice(f: fn()) { f(); f(); }
call_twice(|| { "I am an inferred stack closure"; } );
call_twice(fn&() { "I am also a stack closure"; } );
call_twice(fn@() { "I am a boxed closure"; });
call_twice(fn~() { "I am a unique closure"; });
fn bare_function() { "I am a plain function"; }
call_twice(bare_function);
~~~~
### Unique closures
Unique closures, written `fn~` in analogy to the `~` pointer type (see
next section), hold on to things that can safely be sent between
processes. They copy the values they close over, much like boxed
closures, but they also 'own' them—meaning no other code can access
them. Unique closures are used in concurrent code, particularly
for spawning [tasks](#tasks).
### Do syntax
Because closures in Rust are so versatile, they are used often, and in
particular, functions taking closures are used as control structures
in much the same way as `if` or `loop`. For example, this one iterates
over a vector of integers backwards:
Because closures in Rust are frequently used in combination with
higher-order functions to simulate control structures like `if` and
`loop`. For example, this one iterates over a vector of integers
backwards:
~~~~
fn for_rev(v: ~[int], act: fn(int)) {
@ -976,11 +975,16 @@ fn for_rev(v: ~[int], act: fn(int)) {
}
~~~~
To run such an iteration, you could do this:
To run such an iteration on a block of code, you could call
it with a closure containing a block of code.
~~~~
# fn for_rev(v: ~[int], act: fn(int)) {}
for_rev(~[1, 2, 3], |n| log(error, n) );
# fn do_some_work(i: int) { }
for_rev(~[1, 2, 3], |n| {
#debug("%i", n);
do_some_work(n);
});
~~~~
Because this is such a common pattern Rust has a special form
@ -989,8 +993,10 @@ structure:
~~~~
# fn for_rev(v: [int], act: fn(int)) {}
# fn do_some_work(i: int) { }
do for_rev(~[1, 2, 3]) |n| {
log(error, n);
#debug("%i", n);
do_some_work(n);
}
~~~~